Gas bubble generation for coalescing

ABSTRACT

Apparatus is provided for introducing gas bubbles  30  (usually air bubbles) into a liquid stream  14  to coalesce material such as unwanted bits, or particles, of hydrocarbons that lie in the liquid stream along with wanted dissolved bits of metal, for removal of the hydrocarbons. The apparatus is constructed to produce a large number of bubbles of an optimum range such as 60 to 100 μm which best coalesce the hydrocarbons. A controller ( 110 ) receives the outputs of sensors such as pressure and flow rate sensors (P, F) and uses them to make changes in other parameters such as the pressure of air introduced (at  116 ) into the liquid stream and the pressure in a third conduit  46  of the liquid-bubble stream.

CROSS-REFERENCE

Applicant claims priority from U.S. Provisional Patent Application Ser. No. 61/335,963 filed Jan. 14, 2010.

BACKGROUND OF THE INVENTION

Many processes such as the mining of copper and nickel ore, produce molecule-size bits that are wanted such as dissolved bits of copper or nickel, and also produce undissolved bits or particles of material such as liquid hydrocarbons. Liquid organics (compounds such as hydrocarbons that contain carbon) can be removed from a stream by introducing gas bubbles, which are usually air bubbles, into the liquid stream. In a separation chamber, gas bubbles of a certain size, such as 60 μm to 100 μm (2.4 to 4 thousandths inch) cling to the unwanted organic undissolved particles and allow them to be separated from wanted dissolved bits. The bubbles keep the organic particles that flow into a separation chamber, from flowing into a media bed from which almost all remaining contaminants including organic particles, are removed, Instead, the organic particles with gas bubbles of proper size clinging to them, can be removed from the middle of the separation chamber. This prevents the media bed from rapidly becoming clogged with organic bits, and therefore avoids the need to often clean the media bed.

Gas bubbles, which are herein sometimes referred to as air bubbles, can be produced by flowing pressured air through an air diffuser (“bubble device”) into a pressured liquid stream. The diffuser has one or more tiny holes that emit bubbles into the liquid stream. If the bubbles that enter the separation chamber are too large, the bubbles rapidly float to the top of the separation chamber without clinging to organic particles, and are removed without doing any work. If the bubbles are too small, they rapidly move into the media bed and tend to clog the media bed. Only those bubbles of the proper size such as 60 μm to 100 μm cling to the unwanted particles, or bits, and remain near the middle of the separation chamber from which they are removed. An important problem in the separation of organic particles from wanted bits, is the control of bubble size, so as to maintain a large portion of bubbles of a desired size range that effectively removes organic undissolved particles from a separation chamber.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, an apparatus is provided for the generation of air bubbles in the separation of unwanted undissolved particles or bits, from wanted dissolved bits in a liquid stream, which produces a high proportion of bubbles of the proper size. The apparatus includes a first conduit that receives a fluid stream under pressure that contains the wanted and unwanted bits. The apparatus also includes a source of pressured air that forces air through a diffuser that has tiny holes, to generate bubbles to flow with the liquid stream and through a mixer. The combination emanating from the mixer passes through a pressure dropping device that reduces the pressure of the combination before and during its entrance into a separation chamber. In the separation chamber, bubbles larger than optimum float to the top and are removed, and bubbles smaller than optimum flow into a coalescing media bed and tend to clog it. Bubbles of the proper range of sizes cling to unwanted particles and keep them floating in the separation chamber while they are removed from the chamber. The bubbles of the proper size do not cling to dissolved wanted bits, which pass through the coalescing media bed with minimal clogging of the media,

Applicant maintains a high proportion of bubbles of a diameter on the order of magnitude of 80 μm, and preferably of a size range in the separation chamber which is usually 60 μm to 100 μm, by providing sensors and valves and by providing a controller that varies operating parameters of the system based on the sensor outputs. A valve controls the flow rate and pressure of air that is introduced into the liquid stream to create bubbles of a range of sizes that increase to the desired range. Another valve controls the amount of pressure drop in the liquid-air bubble stream before it enters the separation chamber. If too many large bubbles are present in the separation chamber, the controller operates the pressure dropping valve to increase the pressure of the mixture entering the separation chamber. If too many small bubbles are generated, then the controller operates the pressure dropping valve to decrease the pressure of the mixture entering the separation chamber.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of coalescing apparatus that produces bubbles for coalescing.

FIG. 2 is a side elevation view of an air diffuser for generating bubbles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a coalescing system 10 that includes a first conduit 12 that carries a fluid stream that includes a primarily liquid stream 14 under a pressure P1 such as 70 psi (30 psi to 140 psi) and a flow velocity F1 such as 15 feet per second (7 to 30 fps), In one example, the fluid stream includes dissolved bits of copper and nickel that lie in an acid-water solution such as sulfuric acid and water, along with undissolved particles of hydrocarbons. A second conduit 20 carries gas 22 under a pressure P2 such as 5 psi (preferably 2 to 10 psi) above the pressure at P1 and at a gas flow velocity F2 such as 15 feet per second (7 to 30 fps) from a source 26 of pressured air. The initial pressure at 12 is at least 10 psi and the pressured air or other gas is more than 1 psi greater. The source 26 includes a pump, pressured container 27, or other supply of pressured air and a valve 116 for reducing the pressure. The fluid stream 14 flows across a bubble generator, or diffuser 24. FIG. 2 shows one example of such a device, which is a porous mass. In most cases the gas used to create bubbles is air, and applicant's use of the term air includes any gas. A large number of tiny air bubbles 30 pass downstream out of the bubble device into the liquid stream to a mixer 32 where the bubbles and liquid are mixed. Such a mixer 32 can include a pipe with a screw that has external threads that extend through the pipe. The fluid stream 34 emanating from the mixer and containing liquid, wanted dissolved bits and unwanted undissolved particles or bits, and air bubbles, passes through a pressure-dropping apparatus 40 that reduces the pressure from about 70 psi to perhaps 30 psi in a third conduit 46.

One example of a pressure dropping apparatus 40 includes a tapered conduit portion 42 of increasing diameter, to drop the pressure of the fluid stream passing through it. In addition, applicant includes a controllable variable pressure-dropping device 44 such as a valve with a variable aperture 45 through which the liquid, or fluid stream 50 passes. The liquid stream 50 that exits the pressure-dropping device has a pressure P3 which decreases to 30 psi during a period of about 2 to 5 seconds. During this time the bubbles have entered the separation chamber 72 and are close to or in the middle portion 96 of the separation chamber 72.

The fluid stream 50, which includes the original primarily liquid stream 14 and bubbles, enters a separation device 70 that has a wide separation chamber 72. The fluid stream at 74 in the separation chamber contains bubbles of a range of sizes, with those bubbles of about 60 μm to 100 μm diameter (2.4 to 4 thousandths inch) being the most useful in this application. The separation chamber 72 is used to separate out unwanted particles of organics, which are primarily hydrocarbon particles, from dissolved bits of wanted material such as copper, nickel and cobalt dissolved in acid. The wanted dissolved metal bits preferably move downward through a coalescing media bed 76 that may include a layer 80 of crushed anthracite followed by a layer 82 of crushed garnet. The media bed 76 removes any remaining organic particles and other contaminants, and the wanted bits pass out of the separation chamber through a feed outlet 84.

If only the media bed 76 were used to remove unwanted particles of organics, then the media bed would rapidly clog and would have to be repeatedly cleaned, usually while the process is discontinued. Most of the unwanted organic particles can be removed by air bubbles 90 of the proper size, which are air bubbles of a diameter of 60 μm to 100 μm in this application. The properly sized air bubbles cling to the unwanted organic particles lying in an upper portion 92 of the separation chamber 72 and separate the unwanted particles from the wanted bits, The unwanted particles with bubbles 90 are removed through a removal conduit 88. The properly sized air bubbles cling to the unwanted particles and tend to float them towards the top 94 of the separation chamber about as fast as they tend to flow down with the liquid stream into the media bed. As a result, the unwanted particles remain in the middle portion 96 of the separation chamber so they flow with liquid out of the chamber through the particle removal conduit 88. The flow of unwanted particles and fluid may be treated and dumped into a waste disposal area.

A bubble trap 98 and sensor 99 can lie along the removal conduit (with the trapped bubbles repeatedly removed) to allow the detection of the amount of proper size bubbles that lie in the middle of the separation chamber.

Large bubbles, such as those of a diameter greater than about 100 μm in this application, float to an upper capture portion 102 of the separation chamber that includes the top 94. A sensor 104 senses when a sufficient quantity of the large bubbles have accumulated and operates a removal valve 106 that opens to allow the removal of the large bubbles through a large bubble-carrying pipe 108. In this way, a large bubble sensing device, formed by the trap at 94, sensor at 104, and release valve at 106, senses the amount, or rate of generation, of large bubbles.

It is important to establish the least amount of small bubbles in the separation chamber. If a large quantity of small bubbles (e.g. less than 60 μm diameter) enters the separation chamber then these small bubbles tend to flow down into the media bed and clog it. If too many large bubbles enter the chamber then this results in too few proper size bubbles and results in more unwanted organic particles entering the media bed and clogging it.

The coalescing system of FIG. 1 includes sensors, including pressure sensors P1, P2, P3 and flow rate sensors F1, F2, that sense conditions that affect bubble size in the separation chamber. The coalescing system also includes operable devices including valves 44, 116 that can affect conditions to control bubble size in the separation chamber. A controller 110 of the coalescing system receives the outputs of the sensors and adjusts the operable devices to produce optimum system operation, primarily by producing a large number of bubbles of a predetermined size range such as 60 μm to 100 μm in the middle portion 96 of the separation chamber 72. This involves producing a minimum number of bubbles of a size smaller than the optimum range (which can clog the media bed), and by producing a minimum number of bubbles of a size larger than the optimum range (which interfere with the production of optimum size bubbles).

The rate of production of large bubbles in the chamber, based on the volume of such bubbles, can be measured in a number of ways. One way is by determining the time between occasions when the sensor 104 senses that the capture portion 102 at the top of the chamber is full (e.g. when the sensor senses air instead of liquid). Another way is by sensing the times between the sensor 104 opening the removal valve 106 to allow the escape of bubbles through a large bubble pipe 108. When the controller 110 detects excess production of large bubbles, the controller further opens variable pressure dropping device 44 to decrease the pressure at sensor P3. This can be done by further opening an aperture 45 of the device 40 to allow a more rapid flow of the liquid stream into the separating chamber.

The rate of production of small bubbles can be determined in a number of ways. One way is by capturing bubbles and liquid in conduit 112 that is about to enter the media bed and detecting how often a chamber 114 fills with air (after which the air is released). The volume of smaller than optimum bubbles versus the volume of proper size bubbles can be calculated by the controller 110. If the volume of smaller-than-optimum bubbles is excessive, compared to the volume of bubbles of the proper size, then the pressure of air applied to the second conduit at 20 is reduced to increase the bubble size at 30. The pressure of air at 20 is controlled by pressure valve 116. The controller 110 is constructed to repeatedly measure the volume of the larger than optimum bubbles and the volume of the smaller than optimum size bubbles, in addition to measuring the volume of bubbles in the optimum range (60 μm to 100 μm). The controller is programmed to adjust the air pressure at 30 and to adjust the variable valve 116 to try obtain a minimum volume of smaller than optimum bubbles and a maximum volume of optimum sized bubbles. The volume of large bubbles is allowed to increase moderately, so long as the volume of smaller than optimum bubbles is minimized and the volume of optimum size bubbles is not too small.

If we wish to reduce bubble size (to produce fewer large bubbles) we increase the pressure of liquid (at P3). This is done by opening the valve aperture 45. If we wish to increase bubbles size (to reduce the number of small bubbles that clog the media bed, we reduce the pressure of the liquid (by partially closing valve aperture 45). If we increase air pressure at 22, the bubbles will coalesce and we produce larger bubbles in the chamber.

The rate of air flow through the diffuser 24 into the first conduit 12, determines the range of size of the air bubbles (as adjusted by valve aperture 45). A small flow of air results in small bubbles such as a range of diameters of 10 to 30 μm (a majority of the bubbles are in that range). A larger air flow rate (by increasing air pressure using valve 116) increases the bubble size range such as between 30 to 200 μm, while also increasing the quantity of bubbles and their flow rate. To obtain a limited range such as 60 μm to 100 μm in the chamber 72, we limit the air flow into the diffuser 24 to produce a small initial range such as 10 to 40 μm. Downstream of valve 44, the pressure decreases and the range becomes 60 to 100 μm. If applicant started with a low pressure at 12 and did not use a pressure dropping apparatus 40, the bubble size range would be larger.

The size range of bubbles in a liquid can be the mean (halfway between extremes), median (half larger and half smaller), mode (most frequent size), etc. The size range can be initially determined by taking a sample of the liquid in a tall transparent tube, and allowing the bubbles to rise to a pressured air-liquid surface that lies near the top of the tube. A magnifying glass can be used to determine the sizes of bubbles that rise pass a certain location in the tube. In an alternative, the rate of bubble rise in the liquid indicates the size of the bubbles. A count of the number and size of bubbles per unit time (e.g. second) crossing the certain location can be used to determine the bubble size range. The size range resulting from given parameters (pressure and flow rate of initial liquid, pressure and flow rate of air into a given diffuser, and parameters of pressure dropping apparatus 40) can be noted, and this size range is predicted when the same parameters are in use.

Thus the invention provides apparatus for generating air bubbles and introducing them into a liquid stream containing wanted particles, such as bits of copper and nickel dissolved in a liquid (e.g. acid) and contaminated with organic particles, to produce coalescing that removes the unwanted organic particles. The size of bubbles that will be present in a coalescing chamber is optimized to produce a high volume of optimum size bubbles and a minimum volume of smaller-than optimum sized bubbles, while, as a secondary consideration, producing a minimum volume of larger than optimum size bubbles. A controller is provided that senses the pressure of an initial liquid stream that contains the wanted particles and organic bits in a liquid, but with a large amounts of bubbles. The controller also senses the pressure of air (or other gas) that is introduced into the liquid stream, in addition to sensing the pressure of the liquid-bubble stream after passing through a pressure drop apparatus including its controllable variable pressure drop valve. The controller also senses the amount (e.g. volume) of bubbles of different sizes produced per unit time, as by sensing the volume of bubbles smaller and bubbles larger than optimum. The controller operates valves to increase and/or decrease the pressure of air introduced into the liquid stream and to vary the drop in pressure through and slightly beyond (e.g. 2 to 5 seconds beyond) the pressure drop valve, to obtain a minimum number (and preferably a minimum volume) of smaller than optimum bubbles while obtaining a large volume amount of optimum sized bubbles, preferably with a minimum of larger than optimum sized bubbles.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents. 

1. Apparatus that uses gas bubbles to remove particles from an initial liquid stream, which includes a first conduit (12) that carries said liquid stream under pressure, a source (26) of pressured gas that flows pressured gas through a diffuser (24) that flows initial bubbles (30) into said initial liquid stream in said first conduit to produce a liquid-bubble mixture, and walls forming a separation chamber (72) that receives said liquid-bubble mixture, said walls forming a separation chamber having a large bubble pipe (108) that receives and disposes of large bubbles that float to an upper portion (102) of said separation chamber, comprising: at least one controllable device (116, 40) for varying the pressure of at least said gas in said liquid-bubble mixture; means (104) that detects the amount of large bubbles in said separation chamber that are of more than a predetermined size; a control (110) connected to said means that detects, that operates said at least one controllable device to adjust the pressure of said liquid-bubble mixture when the amount of said large bubbles increases.
 2. The apparatus described in claim 1 wherein: said at least one controllable device includes a pressure dropping device (40) connected between said first conduit (12) and said separation chamber (72), that is controllable to reduce the pressure of said mixture when the amount of said large bubbles increases.
 3. The apparatus described in claim 1 wherein: said at least one controllable device includes a valve (116) of said source (26), that is controllable to apply gas at a selected pressure to said diffuser; said control operates said valve of said source of pressured gas to decrease the pressure of pressured gas that flows to said diffuser when the amount of large bubbles increases.
 4. The apparatus described in claim 1 wherein: said at least one controllable device comprises a pressure dropping device that includes a valve (44) lying between said first conduit and said separation chamber, said valve having a variable size opening (45) and said control operates said valve to change the size of said opening.
 5. The apparatus described in claim 1 wherein: said at least one controllable device comprises a pressure dropping device that has a third conduit (46) of greater cross-sectional area than said first conduit and connected to said first conduit, to drop the mixture pressure in said third conduit, and a variable valve (44) with a variable opening along one of said conduits; said control is connected to said variable valve to increase the size of said variable opening when the amount of large bubbles increases.
 6. The apparatus described in claim 1 wherein: said control is constructed to detect the rate of removal of said large bubbles from said separation device per unit of time, in order to detect the amount of large bubbles.
 7. The apparatus described in claim 1 wherein: said means that detects the amount of large bubbles includes an upper capture portion (102) that lies in an upper portion of said separation chamber and that has a top (94), and a detector (104) that lies below said top and that detects when the volume of said large bubbles extends down to said detector.
 8. A method for controlling the application of gas bubbles to an initial liquid stream (14) that includes undissolved particles and dissolved bits in a liquid, so a mixture of the initial liquid stream and bubbles is produced with a high proportion of bubbles in a certain size range that adheres to the particles to enable the removal of the particles from the mixture, comprising: means (104, 106) for sensing the rate of production of large bubbles of more than a predetermined size and for increasing the pressure of said mixture when the rate of production of large bubbles is greater than a predetermined rate.
 9. The method described in claim 8 wherein: said method for sensing the rate of production of large bubbles includes walls forming a chamber (72) into which said initial liquid stream with particles, bits, and bubbles is directed, said chamber including an upper capture portion (102) that fills with large bubbles, a removal valve (106) that releases gas in said capture portion, and a sensor (104) that senses when said capture portion is filled.
 10. The method described in claim 8 including: means for directing pressured air through a diffuser to produce said bubbles; means (112) for sensing the rate of production of small bubbles that are less than a predetermined size, and means (116) for increasing the flow rate of said air that is directed through said diffuser when the rate of production of said small bubbles is greater than a predetermined rate.
 11. The method described in claim 8 wherein said initial stream has an initial liquid pressure of at least 10 psi, and including: flowing pressured gas at a pressure more than 1 psi above said initial pressure, through a valve (116) into said initial stream, to create bubbles of a predetermined average size; passing said mixture through a pressure dropping apparatus (40) to increase the average size of bubbles in said mixture.
 12. Apparatus that uses gas bubbles to remove particles from an initial liquid stream (14), comprising: a first conduit (12) that receives said initial liquid stream under pressure; bubble generating means that includes a source (26) of pressured gas that forces gas at a selected pressure through a second conduit (20) and through a bubble generator (24) that flows initial bubbles (30) into said initial liquid stream in said first conduit and that creates a mixture of said initial liquid stream and said initial bubbles in said first conduit; a pressure dropping device (40) connected to said first conduit that reduces the pressure of said mixture to produce a reduced the pressure of said mixture (50); a separation device (70) that includes a separation chamber (72) that receives said reduced pressure mixture, said separation device having a purge apparatus (102, 106) that receives and disposes of larger-than optimum size bubbles that float to an upper part (94) of said separation chamber; a control (110) that detects the amount of large bubbles in said separation device, and that operates said source (26) of pressured gas to reduce the pressure of applied gas when the rate of production of large bubbles increases.
 13. The apparatus described in claim 12 wherein: said control includes an upper capture portion (102) of said separation chamber into which large bubbles float, and a sensor (104) lying at the bottom of said upper capture portion that senses when said upper capture portion is filled with said large bubbles. 